Power transmission



April 1944- F. T. HARRINGTON ET AL 2,347,261

POWER TRANSMISSION Originai Filed Oct. 12, 1937 s Sheets-Sheet 1INVENTORS FERRIS T. HARRINGTON, L RAYMOND TWYMAN & ROBIN N BY 2 AMAATTORNEY April 1944- F. T. HARRINGTON ET AL ,347,2

POWER TRANSMIS S ION Original Filed Oct. 12, 1937 3 Sheets-Sheet 2.INVENTORS FERRIS T. HARRINGTON, L RAYMOND TWYMAN & JAMES ROBlfliONTTORNEY April 25, 1944.

Original Filed 0c t. 12;1937

F. T. HARRINGTON ET AL POWER TRANSMISSION FIG. 3

INVENTORS F'ERRIS T. HARRINGTON, L RAYMOND TWYMAN 8 JAMES ROBINSON WATTORNEY s sheets-sheet- 5 Patented Apr. 25, 1944 POWER TRANSMISSIONFerris r. Harrington, L Raymond Twynian, and James Robinson, Detroit,Mich, assignors to Vickers Incorporated, Detroit; Mich, a corporation'ofMichigan Original application October 12, 1937, Serial No. 168,618, nowPatent No. 2,203,354, dated June 4,

Divided and'this application September 23, 1939, Serial No. 296,200

6 Claims.

iating devices, one of which may function as a pump and another as afluid motor. The invention is shown and described as embodied in adevice for feeding strip material intermittently to a blanking press,although it will be understood that this is but one example of many ap-Plications to which the present invention is adaptable. This applicationis a division of application Serial No; 168,618, filed October 12, 1937,now Patent No. 2,203,354, issued June 4,

It is an object of the present invention to provide a hydraulic powertransmission system and control mechanism therefor which may operate aset of pinch rolls for feeding a predetermined length of strip materialfrom a reel into a blanking press. In devices of this character thetiming of the strip movement and its acceleracontrolling the speed of areel so as to operate at a speed which is an average of the intermittentspeed of the pinch rolls.

It is a further object to provide a hydraulic transmission system of thetype including a pump and a motor wherein a novel arrangement of reaversing valves and relief valves is provided which permit utilization ofa single relief valve both for safety protection during normal forwardor reverse operation and also for use as a brake when the load overhaulsth fluid motor during deceleration.

A further objectis to provide a hydraulic power transmission systemwherein a single pump is utilized both for supplying fluid for drivingpurposes and also for supplying fluid for control purposes whereincontrol pressure is made available nism incorporating a preferred formof the present invention. V

Figure 2 is a schematic view of the hydraulic circuits'incorporated inthe feed mechanism of Figure 1 Figure 3 is a schematic view of theelectric circuits incorporated in the feed mechanism' of Figure 1.

Referring now to Figure 1 there is shown a blanking press it having abed I! ca ryi a blanking die I4 and a vertically reciprocating slide l6carrying a'blankin'g punch It. The construction of the press per seforms no part of the present invention. Positioned at one end of thepress is a combined feeding and straightening device 20. Beyond thefeeding-device 20 there is I mounted in a pit 22 a cradle type-unreeler24.

The device 20 includes aseries of straightening rolls 26 which may bemanually adjusted by handwheel 28 and are operated by frictional contactwith the strip 30 which is being unreeled from the device 24. A pair ofpinch rolls 32 contact the strip, the upper roll 32 being urged intocontact with the strip by an adjustable spring 34, the pressure of whichmay be manually relieved when necessary by a hand lever 36. Adjustableside guides 38 and podtion the strip laterally in the rolls 26 and 32.-'I'he1dwer roll 32 is driven by'means of bevel gearing 42, shaft 44,and bevel gearing 46 from a hydraulic transmission indicated generallyat 48, The latter is driven by an electric motor 50 (see Figure 3).

An electric timing and control panel 52 is mounted in the front wall ofthe feeding device switch 60 for initiating a cycle of operationmanual1y, a toggle switch 62 for switching from autoeven during periodswhen the load is overhauling companying drawings wherein a preferredform of the present invention is clearly shown.

In the drawings: Figure l is a fragmentary side view of a blankstripwhich is fed in one .cycle, an adjustable pointer 58 for determining thepoint in the cycle at which deceleration is started, a push button maticcyclic operation to inching operation, a toggle switch 64 for switchingbetween manual initiation of cyclic operation and press controlledinitiation of. cyclic operation, and a control lever 66 for effectinginching forwardly or backwardly when the toggle switch 62 is in inchingposition,

Mounted on the main frame of the press adjacent the slide I6 is a tripswitch 58 operable by a of the slide IE but is ineffective to closeswitch ing press provided with an automatic feed mecha- 68-011 thedownward stroke. Either the switch 68 or the cam may be verticallyadjustable for varying the point in the press cycle at which the switchis closed. a

The unreeling device 24 includes a pair of upstanding side frames 12,each of which carries freely rotatable side flanges 14. Mounted betweenthe side frames 12 in an'arc along the bots tom are a plurality ofcradle rolls 16 driven by a chain 18 from a variable speed hydraulictransmission 80. Idler rolls 82 are ,also mounted between the frames 12for assisting in positioning a reel of strip material 84. Thetransmission 80 is driven from an electric motor 86 (shown in Figure 3)and is provided with a handwheel 88 for varying the speed of the cradle-rolls vI6. A three-way limit switch 90 is mountedadjacent the reel 84and is Provided with an operating lever 92 adapted to be contacted bythe strip 30 when a predetermined amount of slack occurs between theunreeling device 24 and the feeding device 20 (see the dotted lines 94).

Referring now to Figure 2 the hydraulic circult of the powertransmission 48 is there shown diagrammatically. The transmissioncomprises essentially a variable stroke pump 96 anda fixed check valveII2 whence a conduit II4 extends to the pressure side of a relief valveII6. A suction conduit II8 of pump 96 extends into the sump I20 and maybe provided with a filter element I22. In the mechanism of Figure 1, thesump I20 is formed within the frame or housing of the feeding device 20.The valve I08 is provided with a port I24 which connects by a conduitI26 with a port I29 in a solenoid-operated four-way valve I30. A branchconduit I32 extends to the motor 98 and forms the delivery conduitthereto when the motor is operating in a forward driving direction. Aport I34 01 the valve I is connected by a conduit I36 to the reliefvalve I I 6 at the same point where the conduit I I4 I connects thereto.-A third port I38 of the valve I30 connects by a conduit I40 to thedischarge side of a resistance valve I42 whch may be similar inconstruction to the relief valve I I6, but incorporates in addition acheck valve I49 opening to flow from conduit I40 to conduit I44. Thepressure side of the valve I4 2 is connected by a conduit I44 to theopposite port of the motor 98.

Suitable exhaust connections I46. I48, I50 and I52 are'provided at theends of the valves I08 and I30. The valves I08 and I include spools I64and I56 which are shiftable to their lower positions by solenoids C andA and to their upper positions by solenoids D and B. When shifted toeither position the spools are adapted to r main in that position untilpositively operated by the opposite solenoid. The valves I08 and I30 maybe identical in c'onstructiomthe valve I 08 having a port I58 which isplugged, thus making the valve in effect a three-way valve. Thedischarge port of the valve II6 connects to the sump by a conduit I60.

Each of the valves H6 and I42 includes a spool I62 reciprocable in abore 164 and urged downwardly by a s ring I66. At the lower end f thespool I62 there is provided a small piston I68 which is subject topressure at the pressure side of the'valve through a small conduit I10.Whenever, this pressure exceeds the setting of the spring I66, the valvespool is caused to rise opening communication between the pressure anddischarge sides of the valve. The valve I42 is provided with anadditional conduit I12 whereby fluid pressure may at times be admittedto the bottom end of the spool I 62 for positively lifting the valveregardless of thepressure in the conduit I 44.

, For the purpose of providing a controlled acceleration anddeceleration of the motor, the pump 96 is provided with a swinging 'yokeI14 the motion of which is limited by adjustable stops I16 and I18. Alink I 80 connects the yoke I14 to the stem I82 of a piston I84reciprocable in a cylinder I86. A branch conduit I88 extends from thepressure line I04 through a check valve I90 to the rod end of thecylinder I86. A branch I92 extends to a port l94 of a solenoid-operatedthree-way pilot valve I96. A port I98 connects by a conduit 200 to thehead end of the cylinder I86 and by a branch 202 to the control conduitI12 of the valve I42. A spool 204 of the valve I96 is urged downwardlyby a spring 206 but maybe lifted by a solenoid E.- The spool is providedwith a central bore 208 which connects between port I98 and an exhaustport 2I0 when the spool is in its lower position. A clrcimferentialgroove 2I2 connects the ports I94 and I98 when the spool is in itsraised position.

I In operation of the hydraulic circuit shown in Figure 2, the pump 96is operated at constant speed and fluid isdelivered to pipe I04 atvaryingrates depending upon the position of the yoke I14. When the yokeis in its downward position against stop I16, the pump is in maximumstroke position and when it is raised up to the stop I18, the pump is inminimum stroke position which may be very near to its position of zerostroke. If it is desired to operate the motor 98 forwardly with apredetermined acceleration, the solenoids B, D, and E are energized. Thespool 'of the valve I96 is thus lifted admitting pressure fluid throughconduit I88, check valve I90, conduit I92, ports I94 and I98, andconduit 200'to the head end of cylinder I86. Due to the greater area atthis end of the cylinder, the pressure is able to overcome the forceconstantly exerted in the rod end of the cylinder and to force -yoke I14downwardly at a speed determined by the resistance of the conduits I88,I92 and 200. Energization of the solenoid E also admits fluid to conduitI12 of the valve I42 causing the spool I62 to' lift and opencommunication between conduits I44 and I40. With solenoid B energized,spool I56 is lifted. connecting port I20 to port I34, and port I88toexhaust port I52. With solenoid D energized spool I54 isliftedconnectlng port I06 with p rt I24.

Fluid is accordingly withdrawn, by the pump 96 from the sump throughconduit H8 and delivered through conduit I04, port I06, port I24 conduitI26 and branch conduit I32 to motor 98. Fluid returns from the motor 98through conduit I44, valve I42, conduit I40, port I38, port 152 to thesump. The motor 98 is thus caused to operate at a speed which increasesproportionally to the movement of yoke I14 downwardly until, when thelatter reaches the stop I16, the motor 98 is operating at full speed andcontinues to so operate so long as the solenoid E is energized ports I06and I24, conduit ump 96 and neither solenoid A or C is energized. Itwill be noted that under these conditions the pressure line between thepump and the motor is connected to the relief valve II6 from conduit I26through port I28, port I24 and. conduit I36. Should the pressure riseabove a safe value, valve I I6 opens permitting bypassing to the sumpuntil the pressure falls to a safe value.

When it is desired to decelerate the motor 98. solenoid E i deenergizedthus permittin spool 204 to drop under the urge of spring 206 andconnecting the head end of cylinder I86 to the sump through conduit 200,port I88, bore 208 and port 2I0. The :pressure constantly exerted in therod v end of cylinder I66 is then able to lift the piston,

returning yoke I14 to its minimum stroke position at a rate determinedby the resistance of the conduit I88. Shifting of the spool 204 alsoexhausts fluid from under the spool I62 of valve I42 so that the lattertends to close until sufificient pressure is built up in conduit I44 toovercome the force of spring I66. Thevalve I42 is preferably adjusted sothat the pressure in conduit I44 required to open the same under theseconditions is comparatively small but sufllcient to create a backpressure not only in pipe I44 but also in the pressure side Of thesystem including conduits I32 and I04. It is'thus insured that pressureis available in the branchconduit I88 even though the load which isconnected to shaft I02 may tend to overhaul the motor 88. The motor 86is thus caused to slow down at a predetermined rate until its minimumspeed is reached when the yoke II4 strikes the abutment I'I8.

Thereafter if it is desired to stop the motor 88, the solenoid A may beenergized shifting the spool I56 downwardly. This connects the returnconduit I40 through ports I38 and I34, and conduit I36 'to the reliefvalve H6. The motor is thus caused to stop almost instantly because ofthe high pressure required to force fluid through the relief valve I I6.Thus the valve .I I6, which during forward operation functioned merelyas a safety valve on the pressure side of the system, is now connectedto the return side in such a manner as to act as a brake on the motor98. The shifting of the spool I56 also connects port I28 to exhaust portI thus bypassing the pump 96 through conduit I04, I26, ports I28 andI50. Check valve II2 prevents fluid pressure built up in conduit I36from reaching the sump through conduit II4, conduit H0, I25 and portsI28 and I50 under these conditions.

If it is desired to operate the motor reversely, solenoids A and C maybe energized thus shifting both spools I54 and I56 to their lowerposition. Under these conditions fluid is delivered from the throughconduit I04, branch IIO, check valve II2, conduit I86, port I34, portI38, conduit I40, check valve I43, and conduit I44 to the motor 88.Fluid expelled by the motor is delivered through conduit I32, conduitI26, and Jointly through port I28, and port I50 as well as through portsI24 and I46 to the sump. The solenoid E may be energiaed concurrentlywith energization of nolds A and C although for operation Of the stripfeeding device disclosed in Figure 1 it isnever necessary or desirableto drive the pinch rolls backwardly beyond the minimum reeling speed. Itwill be noted that during reverse operation the reliefvalve II6 remainsin communication with the high pressure side of the circuit throughbranch conduit II4. To stop'reverse motion of I II4, relief valve II6,conduit ports I06 and I24, conduit the solescribed, except that nobreaking eifect is produced. The pump is thus bypassed through conduitI04 and ports I06, I24, I28 and I50 while the motor is free to deliveroil through conduits I32 and I26, and ports I28 and I50 totank. While itis coasting it may draw in oil from the supply line I04 through checkvalve II2, conduits H4 and I86, ports I34 and I88 and conduits I40 andFor the purpose of automaticall controlling energization of solenoids A,B, C, D, and E the control panel 52 is provided which is illustrateddiagrammatically'in Figure 3. The timing mechanism which is driven fromthe worm 54 includes a timer shaft 2I3, upon which a ratchet wheel 2 isrigidly secured so that the latterrturns clockwise whenever the pinchrolls are operated in a forward direction; that is, to feed the strip 30into the press. Freely rotatable on the timer shaft 2I3 behind wheel 2is an arm 2I6 carrying a pivoted pawl 2I8 which is snap-acting by meansof an over-center spring 220. The arm 2I6 also carries an upstanding camsurface 222 for operation of certain switch levers later to bedescribed. In the position shown in Figure 3 the pawl 2 I 8 has beensnapped over to its counterclockwise position by means of a fixed. pin224 which projects from the front wall of the timer mechanism into thepath of the tail portion225 of the pawl 2I8. A spiral spring 226constantly urges the lever 2I6 into the position shown in Figure 3. Thespring 226 may be overcome by operation of the ratchet wheel 2 in aclockwise direction when pawl 2I8 is engaged with the teeth thereof.Freely rotatable on the timer shaft 2I3 on the near side of the wheel2I4 are two adjustable arms 228 and 230 upon which the adjustablepointers 56 and 58 are carried. The arm 228 carries a normally openswitch 232 which is adapted to lie in the path of the tail 2250f thepawl 2I8 whereby the switch may be closed when arm 2I6 hasbeen carriedaround to the arm 228 and whereby also the pawl 2I8 may be snapped overto disengage the pawl from the ratchet wheel 2. The am 230 carries anormally closed switch 234 having an operating arm 236 engageable by'thecam 222 after a predeterminedarc of movement of the arm 2I6. Mounttoclose the switch when the arm 2I6 is in the normal or starting positionshown in Figure 3.

The two sides of an electric supply circuit are indicated at 240 and242. The line 242 is connected by a conductor 244 to one side of each ofthe solenoids A, B, C, D and E. The line 240 is connected by a conductor246 to the arm of the toggle switch 62.- When the switch 62 is in itsupper position. that is, the position for cyclic operation, the line 246is connected to conductors 248, 250 and 252. Conductor-248 leads to thearm of toggle switch 64 which is shiftable for press initiated or handinitiated cycles. In its left-hand position in Figure 3, the. switch 64connects conductor 248 to a conductor 254 leading to the switch 68 fromwhich a conductor 256 leads to one side of the switch 288. In itsright-hand position the switch 64 connects conductor 248 to a conductor'25! leading to push button switch 60, the opposite side of which isconnected to the-conductor 256. Switch 238 is also connected by aconductor 2" to one side of solenoid B. The

to normal position.

212 and 216.

conductor 259 extendsto one sideof. the'swit'ch 234, the oppositesidefofwhich is connected by conductor 262 to solenoid The conductor 252extends to the solenoid D and has a, branch conductor 264 extending to;one side of the switch conductor 266 to the solenoid A. v

When the'switch 62 is in its-lower position, that is, the positionforinching operation, conductor'2'46 is connected to conductors 268 and219. Conductor 268 extends to a switch 212, the other .,side of which isconnected by aconductor 214 to the conductor 252. Conductor 219 isconnected to a switch 216, the other side of which is connected by aconductor 218 to the solenoid A. The switches 212 and 216 are mounted ona common insulating stem 289 whichis operable to be depressed to switchclosing position by a cam 282 whenever the lever 66 is in its centralposition, to which the same'is normally biased by centering springs, notshown. The lever 66 also controls two inching switches 284 and 286 whichare closed when the lever 66 is moved to the left or right respectively.Switches 212 and 216 are opened by cam 282 before either switch 284 orswitch 286 is closed. When switch 284 is closed, connection isestablished with the line 249 through conductor 246, switch 62, andconductor 232, the oppositeside of which is connected bya 219 with apair of conductors 283 and 299. Conductor 288 connects to conductor 214leading to conductor 262 and solenoid D.v Conductor 299 connects withconductor 269 and solenoid B. When switch 286 is closed, a lineconnection is established from conductor 219 to conductor 218 and to aconductor 292 which connects with solenoid C.

A pair of conventional motor starting controllers 294 and 296 areconnected in parallel across the lines 242 and 249 by conductors 298 and399. The controllers 294 and 296 may be of the magnetically operabletype having starting push buttons 392 and 364 which energize themagnetic operating mechanism, and stop push buttons 396 and 368 whichbreak the holding circuit for the magnetic operating mechanism. Thethree-way limit switch 99 is connected to the starting controller 296 ina manner to break the holding circuit when the lever 92 is movedclockwise by contact with the-strip material and to makethe startingmagnet circuit when the lever 92 returns In operation of the device as awhole a reel of material 84 may be placed on the cradle rolls 16 and 92between the side flanges 14'-and the end of the material fed through thestraightening rolls 26 and the pinch rolls 32. With the switch 62 ininching position, lever 66 may be operated to the left opening switches212 and 216 and closing switch 284. Solenoids B and D are therebyenergized, the circuit for the solenoid B being from line 249, conductor246,'switch 62, conductor 219, switch 284, conductors 299 and 269through solenoid B and conductor 244 to the return line 242. The circuitfor solenoid D is the same as far as switch 284 and thence by conductors288 and 252 through solenoid D and conductor 244 to the line 242.With-solenoids B and D energized the motor 98 is caused to operate in aforward direction at minimum speed as previously described, driving thepinch rolls 32 and feeding the strip into the press.

' When it is desired to stop the forward motion of the strip 36, lever66 may be movedto midposition, opening'switch 284 ar 1d closing switchesSolenoids A and D are thereby energ'ized, thebircuit-for solenoid Abeing through conductor 246, switch 62, conductor 219, switch 216 andconductor 218- through solenoid A, and conductor 244' to the line 242.The circuit for solenoid D is from switch 62 through conductor 263,switch 212, conductors 214 and 252 through solenoid D and conductor'244' to line 242. With the solenoids A and D energized the motor iscaused to stop.

If the strip 39 has been fed too far before stopping, the lever 66 maybe moved to the right opening switches 212 and 216 and closing switch286. Solenoids A and C are thereby energized, the circuit for solenoid Abeing from. line 249 through conductor 246, switch 62, conductor 219,

' switch 286, conductor 218, solenoid. A, andconductor 244 to the line242. The circuit for solenoid C is the same as far as switch 286 andthence through conductor 292, solenoid C and conductor 244 to the line242. The motor 96 is thereby caused to operatereversely at a minimumspeed until the lever 66 is again returned to mid-position when themotor is stopped as previously described.

-If it is desired to feed the strip 39 into the press in an automaticcycle-of predetermined length, the toggle switch 62 is shifted upwardlyin Fig. 3 and with the switch 64 in its right-hand or hand-initiationposition, the push button 69 may be depressed to cause a cycle ofautomatic operation. With arm 2 l6 in its starting position, as shown inFigure 3, closing of switch 69 ener- 'gizes solenoid B from lin 249through conductor 246, switch 62, conductor 248, switch 64, conductor258, switch 69, conductor 256, switch 238, conductor 260, solenoid B andconductor 244 to'line 242. The solenoid D is energized from line 249through conductor 246, switch 62, conductor 252,

solenoid D and conductor 244 to line 242. The

solenoid E is energized from line 249 through conductor 246, switch 62,conductor 259, switch 234, conductor 262, solenoid E and conductor 244to line 242. The motor 98 is thereby caused tooperate forwardly with apredetermined acceleration as previously described thus causing thestrip 39 to feed into the press at a gradually increasing rate'of speed.As the feed rolls 32 turn, the timer shaft 2l3 which carries ratchetwheel 2, is also caused to turn clockwise carrying with it the arm 2l6.After the pinch rolls 32 have reached their maximum speed, or'possiblyeven before this speed is reached, cam 222 engages 3 time that minimumspeed is reached, the arm 2 l6 reaches a position where the tail 225 ofpawl 2'48 abuts the switch 232, closing the same and snapping the pawl218 out of engagement with the ratchet wheel 2|4. Closure of switch 232energizes solenoid A from line 249 through conductor 246, switch 62,conductors 252 and 264, switch 232, conductor 266, solenoid A andconductor 244 to the line 242. The solenoid D remaining energized, themotor 98 is thereby brought to a quick stop through the braking actionpreviously described. The spring 226 in the meantime returns arm 2H6 tostarting position and the mechanism is ready for a second operationwhenever the push button 69 is'depressed.

For automatic press-initiated operation of the feeding device, switch 64is shifted to its'left-hand position inFigure 3 and reel driving motor59 is adjusted to a speed somewhat greater than the average speed of thestrip 30 through the device 20 and before the press III is started, theumreeling device will operate .to unreel the strip 30 until the switch92 is contacted, thus stopping the motor 50. Thereafter the press l maybe started and as the slide it returns on its upward stroke, cam tripsthe switch 88 which initiates a cycle of operation in exactly the samemanner as was initiated by manual operation of the switch 60. The speedof the press is of course so correlated with the speed of operation ofthe feeding device that the required length 'ofstrip may be fed into thepress during the interval while the dies are open.

For maximum flexibility and usefulness with various sets, of dies in thepress l0, it is necessary that the length of strip which is fed at onecycle be capable of convenient adjustment. This .is provided by theadjustable arms 228 and 230 which are operable from the front of thecontrol panel 52 by setting the pointers I6 and It. The two pointers 56and 58 are preferably kept a fixed distance apart which distance is suchthat the deceleration of motor 98 is just completed at the time the pawl2|! closes the switch 232. This distance should of course be variedwhenever adiustments are made at the stops I'll and Ill, requiring agreater or less time for. the yoke ill to swing between the stops.

While the form of embodiment'of the invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted, all coming within the scope of the claims whichfollow.

what is claimed is as follows: I

1. In a hydraulic power transmission system the combination of a. pump,afluid motor, a fluid circuit connecting the pump and motor, said circuitincluding a pair of directional controlvalves and a relief valve, saiddirectional control valves being shiftable to form within the circuitsupply and return connections for both forward and reverse operation ofthe motor as well as connections to resist return flow from the motorand simultaneously to dump fluid supplied by the pump, said relief valvebeing so connected as to be in communication with the supplyline for therelief valve in communication with the pump delivery orblocking thereturn flow from the motor with the relief valve in communicationwiththe return side of the motor.

3. In a hydraulic power transmission system the combination of a pumpwith an inlet sump tank, a fluid motor, a fluid circuit connecting thepump, motor and tank, said circuit including a relief valve connected torelieve fluid to the tank exclusively, and selector valve means foreither connecting the motor to the'pump with the relief valve incommunication with the pump delivery or resisting the return flow fromthe motor and by-passing the pump with the relief valve in communicationwith the return side of the motor.

4. In a hydraulic power transmission system the combination of a pumpand a rotary fluid motor'for accelerating, driving and decelerating aload device, one of which includes means for varying the displacementthereof, a second fluid motor for operating the displacement varyingmeans, supply and return conduits connecting the pump and the firstmotor, the return conduit leading to a point atatmospheric pressure, acontrol valve for selectively operating the second fluid motor by fluidfrom the supply conduit, and a resistance valve in the return line forcreating back pressure in the supply line for operating the second fluidmotor when the load device is overhauling the flrst motor duringdeceleration.

5. In a hydraulic power transmission system the combination of a pumpand a rotary fluid motor for accelerating, driving and decelerating aload device, one of which includes means for varying the displacementthereof, a second fluid motor for operating the displacement varyingmeans, supply and return conduits connecting the pump and the firstmotor, the return'conduit leading 'to a point at atmospheric pressure, acontrol valve for selectively operatingthe second fluid motor by fluidfrom the supply conduit. and a resistance valve in the return line forcreating back pressure in the supply line for operating the second fluidmotor when the load device is overhauling the first motor duringdeceleration, and means for providing an unrestricted return path fromthe first motor to the pump when the motor is not being decelerated.

6. In a hydraulic power transmission system the combination of a pumpand a rotary fluid motor for accelerating, driving and decelerating aload device, one of which includes means for varying the displacementthereof, a second fluid motor for operating the displacement varyingmeans, supply and return conduits connecting the pump and the firstmotor, the ,retum conduit leading to a point at atmospheric pressure,means for reversing the flow of fluid between the pump and motor, acontrol valve for selectively operating the second fluid motor by fluidfrom the supply conduit, a resistance valve in the return line forcreating back pressure in the supply line for operating the second fluidmotor when the load 'device is overhauling the first motor duringdeceleration, and means for bypassing the resistance valve upon reversedflow in the return conduit.

FER-BIS T. HARRINGTON. L RAYMOND TWYMAN. JAMES ROBINSON.

